Figure 7.

Examples of riboswitch binding sites. (A) Guanidine II riboswitch bound to guanidine (GAI, 5ndh (63)). Step G6–A7, which facilitates GAI (green) binding, was assigned to OP05. (B) S-Adenosyl homocysteine (SAH) riboswitch (3npq, (64)) binding SAH. Step G15–C16 in the close proximity of an adenosyl group in the ligand SAH (green) is unassigned but very close to OP26 and OP15. Step C28–A29 was assigned to IC02 (blue) and step G31–C32 was assigned to OP12. The structure of these NtCs allows binding of a large ligand, in this example SAH, via intercalation and stacking. Drawn by ChimeraX (74).